In Vivo Development of High-Level Fluoroquinolone Resistance in Streptococcus pneumoniae in Chronic Obstructive Pulmonary Disease

Abstract

Patients with chronic obstructive pulmonary disease are generally subjected to multiple regimens of antimicrobial treatment. The development of high-level levofloxacin resistance (i.e., a minimum inhibitory concentration 18 mg/mL) in 8 patients whose previous pneumococcal isolates showed susceptibility is described. Molecular methods were used to characterize the strains and to study the sequential changes in fluoroquinolone targets.The prevalence of fluoroquinolone-resistant Streptococcus pneumoniae remains low in most parts of the world, but it seems clear that, as the use of fluoroquinolones increases, the possibility that resistant isolates will appear will also increase. The tetrameric enzymes DNA gyrase (encoded by the gyrA and gyrB genes) and DNA topoisomerase IV (encoded by the parC and parE genes) are intracellular fluoroquinolone targets. Most levofloxacin-resistant clinical isolates possess single mutations in a discrete region of the genes encoding the ParC and GyrA subunits of topoisomerase IV and DNA gyrase, termed the quinolone resistance-determining region (QRDR). Although there are many reports concerning the prevalence of fluoroquinolone resistance in S. pneumoniae, few reports describe the emergence of this resistance during treatment.S. pneumoniae is a frequent cause of acute bacterial exacerbation of chronic obstructive pulmonary disease (COPD). Patients with COPD are subjected to frequent courses of antimicrobial treatment because of acute bacterial exacerbations. Because previous antimicrobial use has been directly associated with the development of antimicrobial resistance in S. pneumoniae [1], it is not surprising that drug-resistant pneumococci are more prevalent in patients with COPD than they are in the general adult population [2]. This finding prompted us to conduct a surveillance study to analyze the changes in the antimicrobial susceptibility patterns of pneumococcal strains causing repetitive episodes of infection, focusing on fluoroquinolone resistance. The present study describes the development of levofloxacin resistance during treatment, the sequential genetic changes observed in the DNA gyrase and topoisomerase IV of successive isolates, and the persistence of colonization with the same strain over time in patients with COPD receiving fluoroquinolone therapy.From January 1999 through November 2004, we searched for patients who had at least 2 S. pneumoniae isolates that were obtained during episodes of acute exacerbation of COPD. Only patients whose isolates were of the same serotype and genotype and for whom the first isolates were levofloxacin susceptible and the subsequent isolates were levofloxacin resistant were included in the study. The design of the study was prospective and descriptive, because we did not influence treatment or the number of samples requested from the patients included in the study. Some patients had more samples than others, depending on the number of exacerbations of their respiratory process and on the criteria of the pulmonologist or general pract...

Antimicrobial Susceptibilities and Serotypes of Streptococcus pneumoniae Isolates from Elderly Patients with Pneumonia and Acute Exacerbation of Chronic Obstructive Pulmonary Disease

“…Statistically significant differences were found in susceptibilities to penicillin, macrolides, tetracycline, and levofloxacin and in the prevalence of multidrugresistant isolates. This result was expected, as patients with COPD usually receive antimicrobial treatments because of frequent acute bacterial exacerbations and the association between antibiotic consumption and antimicrobial resistance has been demonstrated widely (2,23,26).…”

“…The results of this study suggest that it is due to the latter possibility, that is, that certain serotypes have a greater capacity to remain as commensals in COPD patients during periods without clinical manifestations of infection, thus facilitating their participation in new episodes of AECOPD. This persistence of isolates in the airways of COPD patients during cycles of antimicrobial treatment of acute bacterial exacerbations is known to favor the development of resistance (2,23). An inverse correlation between the prevalence of carriage and invasiveness has been reported (4,5,27,29).…”

Fluoroquinolone-Resistant Group B Streptococci in Acute Exacerbation of Chronic Bronchitis

“…for susceptibility to FQs. This report indicates that FQ resistance among streptococci is a growing concern and that levofl oxacin can select in vivo parC fi rst-step mutants that will facilitate emergence of high-level FQresistant GBS strains, as demonstrated in vitro for S. pneumoniae (9). Finally, although FQ treatment is recommended for high-risk groups with acute exacerbations of chronic bronchitis, these antimicrobial drugs must be reserved for situations in which there are no effective alternative drugs to treat infections caused by multidrug-resistant bacteria.…”

Fitness Costs of Fluoroquinolone Resistance in Streptococcus pneumoniae

“…Fundamental to whether or not high-MIC resistance will be generated in a treated patient is the absolute number of firststep mutants at the time that treatment is initiated. If that number is high enough, double mutants for high-MIC resistance may be present at low densities or generated soon after the start of treatment, ascend to dominance during the course of treatment, and potentially lead to treatment failure (13,14,39,41). If these first-step mutants engender a significant fitness cost, their numbers will remain low, too low for the generation of the second mutation needed for high-MIC resistance.…”

“…Unlike rifampin, for which high-MIC resistance can be achieved by point mutations in a single gene (44), clinically significant resistance to FQ in the pneumococcus requires mutations in at least two genes in the quinolone-resistance-determining regions (QRDR) (7,20,36,42) of the topoisomerase IV genes (parC or parE) and in the DNA gyrase genes (gyrA or gyrB). By pairwise competition, we estimated the in vitro fitness effects of single gyrA, parC, and parE mutants, which in spite of causing only marginal increases in FQ MICs, are of clinical importance as the first step in the generation of high-MIC resistance (16,19,39). We then estimated the contribution to fitness of the second-step mutation at these loci.…”